Electric switches



July 17, 1956 E. H. TAYLOR ELECTRIC SWITCHES Filed Sept. 30, 1954 Inventor Sula/AW A Home y United States Patent ELECTRIC SWITCHES Eric Hartlman Taylor, Buxton, England Application September 30, 1954, Serial No. 459,258 Claims priority, application Great Britain October 8, 1&53

6 Claims. (Cl. 200-416) It is an object of the present invention to provide an improved electric switch operable automatically in one direction but re uiring a positive actuation for setting, i. e. movement in the opposite direction.

According to the invention therefore, there is provided an electric switch comprising one contact movable towards or away from a second, fixed contact, automatic means operable to move the movable contact in one sense, and locking means adapted to restrain said movable contact from return movement in the opposite sense, further means being provided which in operation serve to disable the locking means and permit the movable contact to move in said opposite sense.

The said automatic means may take various forms, but preferably comprise a temperature-responsive element such as a bimetallic member. Such a member may respond to ambient temperature or may carry an electric current upon whose magnitude its temperature depends. In a particularly preferred embodiment, I may employ as the automatic means, a ditierentially stressed system incorporating a bimetallic member as described and claimed in my U, S. Patent No. 2,503,008, or if desired I may employ a bimetallic member as described and claimed in my British Patent No. 657,434 and said member then serves to carry the movable contact.

Various forms of locking means may be used, but if a bimetallic strip is used to carry the movable contact, it is convenient to employ a ball, or other movably mounted locking member, of metal, glass or other suitable material, located in an aperture or guides in a plate or the like and engageable with a free end of the strip adjacent the movable contact. The said further means then includes a releasing member movable behind the locating plate and engaging the ball or the like, said releasing member being such that it may be so placed that it abuts the ball or the like to hold the latter in the path of the end of the strip or may allow the ball to withdraw from said path. Such a releasing member is preferably biased towards the former position and arranged to be held by the ball when in the latter position prior to operation of the automatic means.

Such a releasing member may however be so arranged as not to be locked positively in either position, and the switch may then be operated manually in either sense, as well as being automatically operable in one sense. In this event the releasing member, or a handle or the like connected to it, may be so shaped and disposed as to facilitate its operation in two directions; where however 2,755,357 Patented July 17, 1956 this member is only to be used for resetting it may take the form of a simple push-button.

In order that the invention may be well understood, a preferred embodiment thereof will now be described, with reference to the accompanying drawings, in which:

Figure l is a plan view of a switch embodying the invention, and

Figure 2 is a side view, in section on the line IIII of Fig. 1 showing the switch closed and Figure 3 is a similar side view showing the switch open.

A frame member 1 in the form of a short length of brass channel carries upon its web a bimetallic element 2, the parts 1 and 2 being held together by bolts 3 and nuts 4. The bimetallic element 2 is in the form of a rectangle of sheet in which a U-shaped cut has been made to reduce it to the form of an E with an integral crosspiece 4a bridging its outer legs but leaving the inner leg ib free. The said cross-piece 4a is bent at right-angles to the rest of the element and is the part secured to the web of the member 1.

The upper (as seen in Fig. 2) flange 5 of the member 1 carries, near its ends, bolts 6 upon which a Y-shaped member 7 is supported, the member 7 in turn carrying a fixed contact 8. The bolts 6 are electrically insulated from the member 1 by insulating bushes 9, said bolts 6 passing through oversize holes in the flange 5.

Both said upper flange 5 and the lower flange 10 of the member 1 have central holes receiving a plunger 11, the hole in the upper iiange 5 being somewhat smaller than that in the lower flange 19, to fit the upper portion of the plunger 11 which is of correspondingly reduced diameter. The lower, larger-section portion of the plunger is of length equal to the distance between the inside faces of the flanges 5, 10 plus the thickness of one flange.

The upper end of plunger 11 is threaded (not visible) and a handle 12 of plastic material is screwed thereon. Said handle 12 is of larger diameter than the reduced portion of plunger 11 and provides at its lower end one abutment for a compression spring 13 which is carried around the plunger 11 and is operative between said abutment and the flange 5 to bias the plunger 11 towards its uppermost position.

A steel ball 14 is accommodated in an aperture in the web of the member 1, adjacent the free end of the inner leg 4b of the bimetaliic element 2, and abutting against the plunger 11. The spacing of the parts relative to the size of the ball is such that, when the plunger moves to its uppermost position (Fig. 3) so that its larger-diameter portion will confront the leg 4b, the latter has to be defiected (from the position shown in Fig. 2) up or down to allow room for the ball. Only downward deflection is however possible, on account of the presence of fixed contact 8. It is possible for the leg 4b to remain undefiected if the reduced portion of the plunger 11 is brought opposite said leg, and in this position a contact 15 carried on the leg 4b rests against the fixed contact 8. In this position of the plunger the spring 13 is compressed but the plunger is held against the influence of the spring 13 by the ball 14 which in turn is held against the reduced portion of the plunger by the leg 412.

When the temperature is such as to cause the bimetallic element 4 to move the leg 4b downwardly and separate contacts 8, 15, the said leg releases the ball 14 for the lateral movement and the spring 13 forces the plunger 11 upwards so that the largendiameter portion of the plunger bears against the ball. The ball is then unable to move back and allow the leg 4b to return. Thus said leg is locked in its lower position until plunger 11 is depressed by operation of the handle 12.

The element 2 constitutes a switch actuating member according to my said British Patent No. 657,434 and it will be noted that tne cross-piece has a deformation at 4c which serves to bring the ends of the outer legs p 2,755,357 7 I 7 a closer together than is 'their natural position. This gives rise to stresses in said element which cause it to buckle both along its length and across its breadth and in this condition it moves from one to the other of its positions with a snap action as is desirable in switches. The natural stable positions of the element so stressed will be its downwardly deflected position and a position with a corresponding degree of upward deflection, the former being say the hot position and the latter the cold one. The fixed contact 8 does not allow the element to reach the latter position, when the temperature conditions make the element move that way, and this means that, when the contacts are closed, a not inconsiderable force is provided tending to press the contacts 8, together and thus assuring a good electrical connection thercthrough. It is incidentally a feature of this type of element that a change in temperature tending to move the leg to its downwardly deflected position will cause an increase in contact pressure prior to the actual snap movement.

It will be noted that when the contacts are closed, only a movement of the element 2 allows them to open, as the leg 4b serves to hold the ball 14 against the reduced portion of the plunger 11 so that the larger-diameter portion cannot move up.

Various other changes or modifications may be made without departing from the scope of the invention. For instance, the ball may be replaced by a slidable member with suitable guides, and this would allow the plunger to be placed at a distance from the bimetallic element which would be more convenient if, for example, the latter is to respond to temperature changes within a refrigerator while resetting from outside is desired. The bimetallic element shown may be replaced by other forms of automatic means, not necessarily temperature-sensitive; for example, an aneroid or a Bourdon element may be employed where pressure variations are required to operate the switch.

In the appended claims the term differentially stressed system is used to refer to a flexible bimetallic strip or plate held in compression by stresses applied so that the strip or plate will be caused to buckle out of its original plane in two directions, e. g. across its breadth and along its length, thus forming a system which has a stable position on either side of an unstable position, the strip or plate carrying or having formed integrally therewith a bimetallic leg which serves to control movement of the movable contact of the switch.

What I claim is:

1. A thermally controlled electric switch comprising a fixed contact and a movable contact, a differentially stressed system having a bimetallic leg controlling the movement of the movable contact, the fixed contact constituting an abutment against which the bimetallic leg reacts and assists the system to move in a switch-operating direction when a predetermined temperature change occurs, said movable contact being urged against the fixed contact in a direction opposite to that in which it is ultimately moved by movement of the system through its unstable position, a locating plate having an aperture therein facing an edge portion of the bimetallic leg, a ball disposed in the aperture in the locating plate, a plunger mounted for axial movement transversely across the said aperture, the plunger having two ball-engaging portions of diiferent sizes separated by a shoulder, spring means biasing the plunger towards a position in which the larger ballengaging portion faces the said aperture, the diameter of the ball being such that it serves, before actuation of the system consequent upon the predetermined temperature change, to overlap said shoulder and thereby prevent movement of the plunger into its biased position and, after actuation of the system and consequent release of the plunger and movement thereof to the biased position, said ball serves to latch said leg in actuated position and prevents a return movement of the leg until the plunger is urged against the bias spring so as to bring the smaller portion thereof opposite the said aperture, thereby releasing the ball and allowing the leg to return to its original position and the switch contacts to reclose.

2. An electric switch according to claim 1 wherein said bimetallic leg comprises the middle leg of an E- shaped bimetallic element, and said ball is mounted to engage the free end of said leg.

3. An electric switch according to claim 2 wherein said E-shaped bimetallic element is provided with an integral cross-piece bridging its outer legs and disposed at right angles thereto, the inner leg being free and carrying the movable contact, the cross-piece being deformed to shorten its length and thereby differentially stress the element, the said locating plate being so disposed that the ball engages the free end of the inner leg of the element.

4. An electric switch according to claim 1 wherein said locating plate is provided with a pair of angle flanges at opposite edges thereof, and said plunger is mounted within aligned holes formed in said flanges.

5. An electric switch according to claim 1 wherein said difierentially stressed system is mounted on said 10- cating plate.

6. An electric switch according to claim 1 wherein said plunger is of circular cross-section and said two ballengaging portions are of difierent diameters.

References Cited in the file of this patent UNITED STATES PATENTS 2,191,588 Sattler Feb. 27, 1940 2,318,076 Johns May 4, 1943 2,326,529 Frese Aug. 10, 1943 2,404,352 Armstrong July 23, 1946 

